1. Field of the Invention
The present invention relates to toner used in an image-forming apparatus such as a printer and a facsimile that employ electrophotography. The present invention further relates to an a toner cartridge that holds toner therein and an image-forming apparatus to which the toner cartridge is removably attached.
2. Description of the Related Art
Electrophotography involves well-known photographic processes: charging, exposing, developing, transferring, fixing and cleaning. Among the charging devices is a contact type charging device in which an electrically conductive charging roller receives a d-c high voltage and rotates in contact with an image-bearing body. Among the transferring devices is a contact type transferring device in which an electrically semiconductive sponge roller receives a d-c high voltage and transfers a toner image formed on the image-bearing body onto a recording medium.
Charging device and transferring device usually employ a corona charging device, which requires a high voltage source in the range of 5–10 kV. This high voltage source is very expensive.
A corona charging device is required to be immune to environmental changes because the potential of an image-bearing body varies with temperature. In addition, corona discharge generates ozone, which in turn causes the characteristics of an electrostatic latent image-bearing body to deteriorate. In order to prevent deterioration of the characteristics, an ozone-absorbing filter is mounted to the image-forming apparatus to prevent ozone from escaping from the image-forming apparatus. This ozone-absorbing filter has a short life during which the filter can absorb ozone and decompose the absorbed ozone, and therefore should be replaced once in a while. In order to solve the aforementioned drawbacks of a corona charging device, Laid-open Japanese Patent (KOKAI) No. 63-208878, for example, proposes a contact type charging device. According to the publication, an electrically conductive roller having a resistance in the range of 105–106 Ω is in contact with an electrostatic latent image-bearing body and receives a d-c voltage to charge the surface of the image-bearing body.
Laid-open Japanese Patent (KOKAI) No. 6-19276 proposes a contact type transferring device. According to the publication, an electrically semiconductive sponge roller is employed as a transfer roller and is in contact with an image bearing body with a recording medium sandwiched between the image-bearing body and the transfer roller. The sponge roller receives a d-c voltage to transfer a toner image formed on the surface of the image bearing body onto a recording medium.
One well-known conventional developing device is a two-component magnetic brush developing device. The developing device has a development sleeve with a plurality of magnets that supply a developer material. The developer material includes magnetic powder called “carrier” and a coloring material called “toner” of about 3 to 10 wt %. The developing device requires a toner density sensor for detecting the weight percentage of toner, and a screw and a paddle for mixing and agitating the carrier and the toner. Thus, a developing device is necessarily complex, large, and expensive. The carrier deteriorates over a long time and therefore the carrier replacement is necessary.
In order to solve the drawbacks of the aforementioned two-component magnetic brush developing device, Laid-open Japanese Patent (KOKAI) No. 61-173274 proposes a contact type developing device in which an electrically conductive resilient toner-carrying body i.e., a developing roller having an electrical resistance of less than 106 Ω is in contact with an image-bearing body and receives a d-c voltage to develop the electrostatic latent image formed on the image-bearing body.
A toner-supplying roller formed of an electrically conductive resilient material is in contact with the developing roller to supply the toner held in a toner cartridge.
Japanese Patent (KOKAI) No. 6-19276 proposes a cleaning device that collects residual toner on the image-bearing body, the resilient blade having an edge in contact with the image-bearing body.
However, with the aforementioned image-forming apparatus, the surface of the resilient blade has a roughness of several microns. When spherical toner is used, the toner particles escape through gaps created by the surface having a roughness of about several microns. As a result, the cleaning blade cannot clean the surface of the image bearing body thoroughly.
The edge of a resilient blade is in firm contact with the surface of the image-bearing body during early stage of the lifetime of the printer. Through repetitive printing operations, the edge wears out into a round edge. Therefore, the spherical toner particles easily passes through the contact area where the resilient blade is in contact with the image bearing body, resulting in insufficient cleaning performance.